It is known to arrange in, for example a wall, a fire-proof lead-through for electric conductors by encasing respective conductors in an elastic member in a previously provided hole in the wall, the elastic member having the form of pairs of matching sections arranged to embrace respective conductors. Part of the opening for the elastic member and the conductors is left free to enable pressure exerting devices to be inserted in the hole, by means of which devices the elastic member can be pressed tightly against the portions of the conductors drawn through the lead-through. The elastic member should be capable of expanding extensively when subjected to high temperature, as for example, in the event of a fire.
The usefulness of such methods and devices for constructing a lead-through in the aforementioned manner is greatly limited, and said methods and devices give rise to a number of disadvantages of a technical and economic nature, as will be apparent from the following. For example, the known methods and devices can only be applied when a small number of conductors are to be passed through a building structure, such as a wall, and are less suitable for use with a large number of conductors. Thus, the known methods and devices are most unsuitable for lead-throughs in telephone exchanges for example, where it is necessary to provide fire-proof lead-throughs for cable bunches comprising several hundred cables. In such cases unreasonably high forces would have to be exerted on the elastic member in order to meet standard requirements with regard to the tightness with which adjacent cable portions are packed.
Furthermore, the pressure forces applied to the cables are distributed differently over different cables, whereby a number of the cables are subjected to forces of such magnitude as to cause risk of cross-talk between the conductors within the cables. The support afforded the cables by such a lead-through is also partly dependent on the ratio between the cross-section area of the opening and the depth (wall thickness) of the lead-through. As mentioned above, the construction of a lead-through is complicated when it is to receive a large number of cables and such construction would necessitate the use of auxiliary means.